Data Checks and Processing Performed by CDIAC
An important part of the NDP process at the Carbon Dioxide Information Analysis Center (CDIAC) involves the quality assurance (QA) review of data before distribution. Data received at CDIAC are rarely in a condition that permits immediate distribution, regardless of the source. To guarantee data of the highest possible quality, CDIAC conducts extensive QA reviews that involve examining the data for completeness, reasonableness, and accuracy. Although they have common objectives, these reviews are tailored to each data set and often require extensive programming efforts. In short, the QA process is a critical component in the value-added concept of supplying accurate, usable data for researchers.
The following information summarizes the data-processing and QA checks performed by CDIAC on the data obtained during the R/V Thomas Washington TUNES-3 Expedition in the South Pacific Ocean (WOCE Section P16C).
- Carbon-related data and preliminary hydrographic measurements were provided to CDIAC by Catherine Goyet of WHOI and Peter Guenther and Dave Keeling of SIO. Hydrographic measurements and the station information files were provided by Lynne Talley of SIO and by the WOCE Hydrographic Program Office after quality evaluation. A FORTRAN 77 retrieval code was written and used to merge and reformat all data files.
- The designation for missing values, given as "9.0" in the original files, was changed to "999.9."
- To check for obvious outliers, all data were plotted with a PLOTNEST.C program written by Stewart C. Sutherland (LDEO). The program plots a series of nested profiles, using the station number as an offset; the first station is defined at the beginning, and subsequent stations are offset by a fixed interval (Fig. 5 and Fig. 6). Several outliers were identified and removed after consultation with the principal investigators.
- To identify "noisy" data and possible systematic, methodological errors, property-property plots for all parameters were generated (Fig. 7), carefully examined, and compared with plots from previous expeditions in the South Pacific Ocean.
- All variables were checked for values exceeding physical limits, such as sampling depth values that are greater than the given bottom depths.
- Dates and times were checked for bogus values (e.g., values of MONTH < 1 or > 12, DAY < 1 or > 31, YEAR < or > 1991, TIME < 0000 or > 2400).
- Station locations (latitudes and longitudes) and sampling times were examined for consistency with maps and cruise information supplied by Lynne Talley.